Oil and gas wells are often drilled horizontally through non-permeable shale formations. In order to extract the hydrocarbons from these formations, the shale rock is hydraulically fractured to enable fluid flow. The resulting fractures extend radially from the wellbore for a limited distance, which creates a production envelope around the wellbore. Since this envelope covers a finite volume, it is necessary to drill multiple horizontal wells within a reservoir in order to recover the full potential of the available hydrocarbons. The spacing between the drilled wellbores is usually determined by the estimated fracture propagation distance that extends outward from the wellbore. Ideally, wellbores should be placed so that the entire space between wellbores is fractured without any overlap. However, there is significant uncertainty in wellbore position when determined from traditional directional surveying technologies. This makes it quite challenging to place wellbores at precise spacing intervals unless operators use enhanced survey management solutions that reduce the positional uncertainty of the wellbore.
Measurement While Drilling (MWD) and Gyro tools are the most commonly used directional surveying instruments for determining wellbore position. These tools have numerous error sources that can cause significant inaccuracies in survey measurements and wellbore placement. FIGS. 1A and 1B show an example of how wells that were planned to be parallel (14 in FIG. 1A) may actually end up meandering off plan (14′ in FIG. 1B), due to standard surveying errors, leading to unclaimed resources (16 in FIG. 1B) in the reservoir where the wells diverge and neighboring wells (18 in FIG. 1B) competing for the same production envelope. Even though it is known that survey error impacts wellbore placement in a reservoir, survey error is generally not considered when planning well production. This means that the impact of wellbore placement errors on reservoir recovery for different surveying methods is often unknown and not taken advantage of when selecting the survey method to use in drilling the wellbores.